There has been growing demand for solid state materials with dimensions in the range from 1 to 100 nanometers (nm). These nanoscale particles have been found to exhibit unusual chemical, mechanical, electrical, magnetic and optical properties that are different from the corresponding properties of the bulk material and conventional powders. These unusual properties can be exploited in a number of applications.
One advantage of nanoparticles relative to larger particles is the increased surface area for a given weight of material. The surface area per weight of nanoscale particles can be one or two orders of magnitude greater than the surface area per weight of conventional powders. This increase in surface area is desirable for a variety of applications such as those involving catalysis, hydrogen storage and electrical capacitors.
A variety of nanoparticles have been produced using a pyrolytic reaction of chemicals in the gas phase. For example, laser pyrolysis has been used to produce nanoparticles of carbon black, .alpha.-Fe, Fe.sub.3 C and Fe.sub.7 C.sub.3. These were described in the following two references: Bi, et al., J. Mater. Res. 8:1666-1674 (1993) and Bi, et al., J. Mater. Res. 10:2875-2884 (1995).